Engine down thrust.

[Jim Morris]

Im just finishing up my new Avanti project. I had the engine temp. installed and was shocked to notice I had up thrust in the engine. What the heck can I do? I put in some Brodak nylon shims to bring the nose down some, now the spinner doesnt line up. Does anyone make a type of wedge out of some other material like aluminum or carbon fiber? This really chaps me. I really took great pains to get it right.

[PatRobinson]

Jim,
I see no one else has replied so I will give it a try. I thought about this problem for  awhile before answering.  If it was me I would trim the mount till it is flat and true and then I would shim with a thicker aluminum engine
pad to restore the engine mounting surface back to the measured thrust line.
The thicker aluminum pad will also re-enforce the the thinned down maple
mount rail. The problem you may still end up with is angle of the transition from the spinner to the front part fuselage nose section may no longer line up perfectly but i don't see any way around that other than sanding.
My reason for doing it this way is if you use shims and you remove the engine for routine maintenance you might wonder if you got them exactly
right when you put it back in. I think a flat and true will make life easier over the long haul.
Hope this helps you find a solution even if it won't help your frustration.
                                   I wish you the best of luck,
                                            Pat Robinson
 

[Keith Spriggs]

Jim, Did you get my PM with information on solving your thrust line adjustment problem?

[Jim Morris]

Yes Keith, thank you, but I have some good news. I went and bought an incidence meter and checked it.Lo and behold it is correct. This must be an optical illusion. So Im happy now and I will procede. Thank you also Pat. I would like to know how I would get down inside to remove material,just for information purposes.

[PatRobinson]

Jim,
I can't remember how much of the engine mount  is made accessible when you remove the cowl on an Avanti but some of the precision sanders available from MicroMark and other places should be able to get into the space. If you had a lot of material to hog off you could use a moto-tool with a cable extension which should be able to get into a small space. I am not sure which bit to reccomend you just have to try it out. When you get closer
 to the line then go at it with the sander til it is flat.   
Maple being wood has a mind of it's own and it can bow or curve just when you don't want it to do so. I am in the middle of building a second engine crutch because after I went to the trouble of truing everything straight, parallel and square on a crutch , I went back a few days later and found it was no longer straight and true. I guess the material I removed to true it up released tension in the wood created by the woods grain that caused it to bow.
 Jim I am glad you don't have to do the job on your mounts because it would have been a tedious and time consuming job. Good for you!
                                                        Best of luck,
                                                       Pat Robinson

[Wayne Collier]

"wood has a mind of its own"
I'm no expert but I have worked with wood for a lot of years.  While warping after shaping can be a release of tension problem it is often a moisture problem.  Newly exposed grain can soak up water from the air and swell pushing a curve into the piece.  There are times when a coat of sanding sealer can be used to seal out (or seal in) moisture and help maintain the shape of a piece.  A while back I read about a wooden boat that had been in dry dock long enough to really dry out.  Forgetting that the wood needed to have time to regain moisture workers just shoved it back into the water.  It sank before the boards could swell enough to seal up the leaks.  On old wooden ships swabbin' the deck wasn't just for cleaning.  It helped the boards maintain proper fit.